In fiber optic systems, optimization of coupling efficiency between the optical fiber via the fiber""s endface and active and/or passive devices is an important metric for comparison at the system level. A popular technique for improving coupling efficiency includes providing a lens at the fiber endface. This lens can be formed by drawing or etching the fiber. Generally, however, fiber-polishing techniques yield the best and most consistent fiber lens profiles.
Fiber polishing, however, often yields sharp surface features or microscopically rough surfaces. To smooth these features and round-over sharp corners, it is common to expose the polished fiber lens to a fusing step.
The typical approach to fusing is to carefully monitor the positioning of the fiber endface between the fuser electrodes in combination with optimizing the fuser current and fusing duration. A similar approach can be used with flame fusing. After repeating many experiments, an experienced technician can generate fiber lenses with good profiles at acceptable yields. It is further common to include visual inspection techniques between fuser exposures to monitor the progress of the fusing operation.
The present invention concerns a method and system for fusing an optical fiber lens.
The system is compatible with automation. Specifically, the fusing of the fiber lens is controlled in response to a diffraction pattern of light exiting from the fiber lens. This diffraction pattern is indicative of the lens shape and characteristics. Further, it is generally easier to assess the lens shape from the diffraction pattern rather than visual inspection.
In general, according to one aspect, the invention features a method for fusing an optical fiber lens. This method comprises injecting light into an optical fiber and detecting a diffraction pattern of the light exiting from a fiber lens at a proximal end of the optical fiber. The fiber lens is then fused in response to this diffraction pattern.
In the preferred embodiment, the step of injecting light into the optical fiber comprises energizing a laser that is coupled to a distal end of the optical fiber. In an alternative embodiment, a technique similar to that used in fiber coupling may be used where the fiber is bent and light injected into the core through the cladding.
According to other aspects of the preferred embodiment, the step of detecting the diffraction pattern comprises detecting a far-field diffraction pattern. This is preferably performed using a two-dimensional detector, such as a CCD camera detector that is located optically in front of the fiber lensxe2x80x94the detector need not be located physically in front of the fiber lens if there is intervening fold optics, for example.
In one present embodiment, the diffraction pattern is analyzed by determining a ratio of a lateral size to a transverse size of the diffraction pattern. The fiber lens is exposed to a fusing arc until the ratio of the transverse to lateral size reaches a desired ratio.
In general, according to another aspect, the invention can also be characterized as a system for fusing an optical fiber lens. This system comprises a light source that injects light into an optical fiber and a detector that detects a diffraction pattern of a light exiting from a fiber lens at a proximal end of the optical fiber. An arc fuser is disposed to fuse this fiber lens. A controller activates the fuser in response to the diffraction pattern detected by the detector.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will is be understood that the particular system and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.